Experimental Study Of Bending Loss In Single-mode Fiber

With the rapid development of fiber-to-the-home (FTTH) technologies, the research focus has been partially shifted to bend insensitive fibers (BIFs) which can reduce bending losses at sharp bending radii (generally<10mm). BIFs implemented in FTTH optical network would save installation costs as well as improve system performance.In this paper, we compare the bending performance of step-index fiber and trench-assisted fiber with analytical method. For the trench-assisted fiber, the structural and optical parameters are systematically investigated to improve both bending performance and mode field diameter (MFD). Based on theoretical study, a BIF sample is successfully fabricated. The bending losses and cutoff wavelengths of SMF-28^ G.657A1、G.657A2、G.657B and homemade BIF sample are experimentally characterized.Theoretical study shows that, the trench-assisted fiber has better bending performance than step-index fiber. For the trench-assisted fiber, with the increase of the distance between the core and trench, there is an optimal point offering possible lowest bending loss. The distance between the core and trench plays an important role in optimization of fiber structure. The experimental results show that, when the wavelength is fixed to 1550nm, the bending loss of BIF is down to 0.052dB/turn at bending radius of 5mm. Compared to SMF-28, the bending performance of BIF has been greatly improved. With the bend radius increase, bending losses gradually reduced. Moreover, bending losses increase as the wavelength increases, and the experimental results agree well with the theoretical results. The theoretical and experimental results show the bending performance of BIF is better than G.657B followed by G.657A2, G.657A1 and SMF-28; meanwhile BIF meets the requirements of cutoff condition, dispersion and MFD according to ITU-T recommendation. Not only the low index trench but also the optimization of other fiber parameters can improve the bending performance at small bending radii. This study may be important for the design and fabrication of BIFs.